The brightness of bleached paper products can be increased by adding fillers such as titanium dioxide and fluorescent whitening agent to the paper or coating the paper with such products. However, the use of fluorescent whitening agents is usually more economical, and is therefore progressively becoming more common than the use of titanium dioxide.
On the other hand, the use of known fluorescent whitening agents is not free from biological and environmental consequences. This becomes of particular importance when applied to the manufacture of paper products which are to be placed in contact with edibles such as foods and the like.
At the present time there are no known fluorescent whitening agents of low biological and environmental impact which are being used in the manufacture of paper products in the food industry in the United States.
Only one fluorescent whitening agent has, to the present time, been approved by the Food and Drug Administration (FDA) for use in food related applications. This agent is manufactured by Ciba-Geigy and sold as Uvitex OB. The product is highly insoluble in water and is marketed as a plastic additive (U.S. Pat. No. 4,642,322 to Wehner et al).
Anthranilic acid and various derivatives thereof have been known, as are known their low toxicity and high fluorescent characteristics.
U.S. Pat. No. 4,642,322 referred to above discloses the addition of anthranilic acid amide as a stabilizer to thermoplastics. Titanium dioxide is also utilized by this patent. However, the product is provided not as a coating formulation for use in paper products but as a thermoplastic for use in plastics.
Amino benzoic acids have been disclosed as being useful for the preparation of polybenzamide in the presence of metal halides. U.S. Pat. No. 4,696,999 discloses such products as well as amino benzoic acid esters for use in the synthesis of polybenzamides. The amino benzoic acids and esters thereof described in this patent are, however, meta- and para-amino compound, and are therefore positional isomers of the esters and acids of this invention. In addition, this patent proposes the use of these compounds to form pulps of short fiber materials with high stability values. This patent also discloses in Example A a condensation reaction of 4-aminobenzoic acids with titanium chloride but nowhere is there a disclosure of use of the compounds in paper products.
U.S. Pat. No. 4,481,186 to Speakman describes a co-polymer pigment dispersant suitable for use in the preparation of paints and para-aminobenzoic acid is one of the components utilized. Another component is titanium dioxide which is used as a pigment for color. No mention of any utility in terms of the utilization of the products for coating paper is stated.
Aminobenzoic acid is also used in admixture with a coloring agent such as titanium dioxide for the preparation of cosmetic and skin treatment composition in U.S. Pat. No. 4,481,186. The prior art cosmetic and skin treatment compositions are generally speaking coating formulations but they are not paper whitening coating compositions.
A condensate of para- or meta-aminobenzoic acid and titanium dioxide is disclosed in U.S. Pat. No. 4,607,703. These materials are incorporated into molding polyamide compositions but are not suggested for use in paper coatings.
Titanium dioxide is used as a pigment and 4-aminobenzoic acid as a compound capable of providing an activated ester group in the preparation of self cross-linking heat-curable grinding resins in U.S. Pat. No. 4,539,385. No mention of paper coatings in this patent can be found.
Fluorescent whitening agents work by emitting bluish light upon excitation in the long ultra violet region (about 350-400 nm). This light can compensate for the yellowness inherent to paper products.
For example, methyl anthranilate and methyl N-methyl anthranilate have been reported to be non-mutagenic in short-term microbial assays (Shimizu, H. and Takemura, N., "Mutangenicity of Some Aniline Derivatives", in Orford, R.R., Cowell, J.W., Jamieson, G.G., and Love, E.J., editors, "Occupational Health in the Chemical Industry", pp 497-506, MEDICHEM Calgary 1983 Association, Calgary (1983)).
There is thus a real need for a low toxicity, low cost whitening agent suitable as a paper additive for use in packaging intended for use in the food industry.